1. Field of the Invention
This invention relates to improvements in methods and apparatuses for use in conjunction with hard disk drives of the type used in computer related applications, and more particularly to improvements and methods for use in braking such drives upon the occurrence of a power fault, or the like, and still more particularly to improvements in methods and apparatuses for braking the spindle of the motor of the drive after a delayed time sufficient to enable the read/write heads of the disk drive to be properly retracted.
2. Relevant Background
In the operation of hard disk drives, for example, in computer applications, certain protocols are often employed to control the braking of the motor which spins the disk drive. In usual operation, a hard disk drive has one or more heads, which record and/or read magnetic fields that represent data in a known manner onto a recording media on one or more rotating disks of the disk drive. The heads are positionable to precise radial locations by a "voice coil motor", which controls the movement of arms on which the heads are carried. When the disk is at rest, the heads normally ride just resting on the disk; however, when the disk is spinning, air forces generated between the disk and the heads cause the heads to float a small distance above the magnetic media.
Thus, when the rotation of the disk drive is stopped, the air force also stops, allowing the heads to fall into contact with the magnetic media. If the heads come into contact with the media while there is still some movement of the media, wear or damage may result, both to the recorded area on the media and to the heads.
Consequently, means have been proposed to position the heads over a "landing strip" portion of the disk, so that only that strip is damaged by a head falling onto the disk. Nevertheless, it will be appreciated that repeated contact between the disk and head will eventually wear upon the head, as well. Some manufacturers, in fact, recommend a computer not be powered down to avoid the type of damage that such contact causes.
Once the heads are in place and the disk drive is powered down, it is sometimes possible for the head mechanism, which is now in contact with the disk media, to move if the computer is moved, for example, as would be anticipated in portable or laptop type computers. Consequently, some manufacturers also provide for a locking mechanism, usually mechanical in construction, to hold the heads in a landed position over the landing strip. Some types of such locking mechanisms require an extra bit of electrical energy, just as the head reaches the landing position to overcome the mechanical restraint to bring the heads into their locked position.
In the event of a loss of power, to prevent the heads from landing on portions of the magnetic media other than the designated landing pad, often when a power failure is detected, the motor spinning the disk is allowed to continue to turn under the inertia of the various masses of the drive. As a result, the motor coils generate their own counter- or back-emf. The coils of the spinning motor are then connected to deliver the voltages generated by the counter-emf produced in the motor windings to operate circuitry and to provide the energy to the voice coils necessary to drive the heads to the landing strip.
Once the heads are positioned over the landing strip, the motor is then braked to stop its rotation as rapidly as possible, so that the time in which the head may contact the disk is minimized. Such braking, of course, requires additional energy. It can therefore be seen that design considerations need to be implemented to insure that a sufficient amount of energy is generated to move the heads completely to the landing strip, including the locking position, if necessary, to avoid a premature landing on an unwanted portion of the disk media. During this landing period, sufficient rotational speed of the motor must be provided to ensure a sufficient air flow to maintain the vertical position of the heads over the disk media.
However, once the heads are properly positioned, the motor must be rapidly stopped. This is ordinarily done by grounding sets of the driver transistors (or connecting them to a particular potential, such as V.sub.CC). This causes the magnetic fields generated in the motor windings by the free-spinning rotor to resist its rotation, which rapidly brings the disk to a stop. However, if the disk is stopped too soon, the heads may not reach their landing strip position, which may result in undue skidding of the heads on the surface of the disk. On the other hand, if the driver transistors are shorted while the motor is still spinning too rapidly, excessive currents can be generated in the driver transistors, which may burn them out.
In the past, in order to coordinate the motor braking with the retract positioning of the heads, as the motor lost speed, for instance if a power fault occurred, its slowing speed was estimated using an RC circuit. In such circuit, the capacitor began its discharge upon loss of power. When the voltage discharged to a predetermined level, a braking circuit was activated. However, such RC circuits generally require relatively large components, since the braking time is relatively long, for example, on the order of seconds. Such components were provided off-chip, that is, were not included on the integrated circuit chip on which the remaining of the driver circuitry to position and control the head mechanism.
What is needed, therefore, is a method and apparatus for braking a disk of a hard disk drive, or the like, using components that may be located on the same integrated circuit chip as the motor driver circuitry or circuitry to position and control the head mechanism, and which controls the retract operation of the head mechanism in response to the actual slowing speed of the motor.